Vent assembly

ABSTRACT

A vent valve apparatus ( 10 ) for use with a system for supplying breathable gas pressurised above atmospheric pressure to a human or animal. The apparatus ( 10 ) includes a gas washout vent ( 15 ), a vent valve ( 18 ) adapted to progressively restrict the flow area of the washout vent ( 15 ), and a pressure sensitive vent valve control means ( 20,22,23 ). The control means is adapted to progressively cause the vent valve ( 18 ) to restrict the flow area of the gas washout vent ( 15 ) in response to increases in the pressure of the gas supply, thereby substantially regulating the volumetric flow of gas and/or CO 2  gas through the washout vent ( 15 ) over a range of gas supply pressures.

FIELD OF THE INVENTION

The present invention relates to a vent valve apparatus for use with asystem for supplying breathable gas pressurised above atmosphericpressure to a human or animal.

The invention has been developed primarily for use in controlling theventing of washout gas in a continuous positive airway pressure (CPAP)gas delivery systems used, for example, in the treatment of obstructivesleep apnea (OSA) and similar sleep disordered breathing conditions. Theinvention may also be used in conjunction with suitable mask and gasdelivery system for the application of assisted ventilation treatment.

The term “mask” is herein intended to include face masks, nose masks,mouth masks, appendages in the vicinity of any of these masks and thelike.

BACKGROUND OF THE INVENTION

Treatment of OSA by CPAP flow generator systems involves the continuousdelivery of air (or breathable gas) pressurised above atmosphericpressure to a patient's airways via a conduit and a mask. CPAP pressuresof 4 cm H₂O to 22 cm H₂O are typically used for treatment of sleepdisordered breathing due to OSA and/or central apnea, depending onpatient requirements.

Treatment pressures for assisted ventilation can range up to 32 cm H₂Oand beyond, depending on patient requirements.

For either the treatment of OSA or the application of assistedventilation, the pressure of the gas delivered to patients can beconstant level, bi-level (in synchronism with patient inspiration andexpiration) or autosetting in level. Throughout this specification thereference to CPAP is intended to incorporate a reference to any one of,or combinations of, these forms of pressure delivery.

The prior art method for providing CPAP treatment includes a vent forgas washout of the as flow. The vent is normally located at or near themask or in the gas delivery conduit. The flow of gas through the vent isessential for removal of exhaled gases from the breathing circuit.Adequate gas washout is achieved by selecting a vent size andconfiguration that will allow a minimum safe gas flow at the lowestoperating CPAP pressure, which, typically can be as low as, around 4 cmH₂O for adults and 2 cm H₂O in paediatric applications.

Existing vent configurations include single or multiple holes, foamdiffusers, slots and combinations thereof. A reference herein to a ventmay be understood to include a reference to one or more holes, foamdiffusers, slots or any combination of them.

The flow of gas from the gas delivery system through the vent toatmosphere creates noise as the delivered gas, and upon expiration thepatient expired including CO₂, passes through the vent. Increasing CPAPpressure results in more gas passing through the vent which in turncreates more noise. Existing prior art vents produce excessive noisewhen CPAP pressures are raised above about 4 cm H₂O. This noise canadversely affect patient and bed-partner comfort. Existing vents arealso inefficient as they allow more as through the vent than is requiredfor adequate exhaust gas washout and thereby require the flow generatorto provide more flow than is necessary in order to maintain the requiredtreatment pressure. Further, where treatment gas is being supplied, suchas oxygen, surplus treatment gas is vented and thereby wastedunnecessarily. A similar waste occurs where the supplied gas ishumidified.

It is an object of the present invention to overcome or at leastameliorate one or more of these deficiencies of the prior art.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a vent valve apparatus for use witha system for supplying breathable as pressurised above atmosphericpressure to a human or animal, the apparatus includes a gas washoutvent, a vent valve adapted to progressively restrict the flout area ofthe washout vent, and a pressure sensitive vent valve control meansadapted to progressively cause said vent valve to restrict the flow areaof the gas washout vent in response to increases in the pressure of thegas supply, thereby substantially regulating the volumetric flow of gasand/or CO₂ gas through the washout vent over a range of gas supplypressures.

Preferably, the system supplies breathable gas to a human patient.

The breathable gas is desirably air.

In an embodiment of the invention, the gas washout vent consists of anorifice having the shape of an outwardly diverging truncated cone andthe vent valve is a complementary cone shaped plug. The rim of the coneshaped orifice acts as a valve seat for the cone shaped plug.

Desirably, the pressure sensitive vent valve control means includes anelastic diaphragm connected to the vent valve such that displacement ofthe diaphragm results in displacement of the vent valve. In anembodiment, the diaphragm is produced from a rubber or other elasticdiaphragm stretched over a circular orifice. The vent valve ispreferably connected to the rubber by a connection means that allows forthe stroke of the vent valve to be adjusted.

The vent valve is desirably attached to the centre of the rubberdiaphragm by a connection means such as a rod, the rod being operativelyconnected to both the vent valve and the diaphragm.

In a preferred embodiment, the vent valve and diaphragm are directlyconnected by the rod. The rod is preferably rigid, such that movement ofthe diaphragm is directly proportional to the movement of the ventvalve.

In another embodiment, the connection means include a lever assemblyconnecting the vent valise to the diaphragm so as to permit differingratios of movement and mechanical advantage of the vent valve relativeto the diaphragm.

Such an assembly can include a tension means that opposes the movementof the diaphragm caused by increasing gas supply pressure so as to biasthe vent valve to a position where the flow area of the orifice ismaximised.

It will be understood that the orifice covered by the diaphragm need notbe circular and can be any convenient shape.

In one preferred configuration, the vent valve apparatus is provided ina branch connection from a mask. In another preferred configuration, thevent valve apparatus is provided in an air supply conduit substantiallyadjacent the mask.

In a further embodiment, the vent valve apparatus includes anaerodynamic member such as an aerofoil or wing. The member is disposedin the air supply conduit by a biased pivot mechanism and has an axis ofrotation transverse to the direction of gas flow. Gas passing throughthe conduit causes the aerodynamic member to generate lift and to berotatably displaced in proportion to the velocity of the gas flowingthrough the conduit. As the gas velocity increases the aerodynamicmember produces increase lift and the resulting rotational displacementis transmitted to the vent valve which restricts the flow area of thewashout vent. The vent valve is preferably biased open to a maximumwashout vent flow area by a tension means such as a spring.

In a further preferred embodiment an aerodynamic member is suspended ina branch of the conduit and adapted for rotation about an axistransverse to the branch. Rotation around the axis is in response to thegas flow, which is proportional to the pressure in the conduit. Themember is connected to the vent valve such that as the pressure in theconduit increases the rotational displacement of the aerodynamic membercauses corresponding movement of the vent valve, resulting in areduction of the flow area of the washout vent. A tension means isadapted to bias the vent valve, such as a spring, operates on theaerodynamic member to oppose the rotation caused by the gas flow on theaerodynamic member. The tension means biases the aerodynamic member in arotational direction opposite to the direction induced by the gas flowentering the branch from the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic sectional side view of a vent valve apparatusaccording to the first embodiment of the invention;

FIG. 2 is a schematic sectional side view of a vent valve apparatusaccording to a second embodiment of the invention; and

FIG. 3 is a schematic sectional side view of a vent valve according to athird embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a vent valve apparatus 10 accordingto a first embodiment of the invention. The vent valve apparatus 10 isconnected to a mask (not shown) at 12. The mask is adapted to receive acontinuous supply of gas 13 above atmospheric pressure from a flowgenerator (not shown) through a flexible conduit 14. The apparatus 10includes a gas washout vent, in the form of a substantially conicalorifice 15 formed in a wall 16 of the pipe branch 17, and a vent valvein the form of a substantially conical plug 18. The rim 19 of theorifice 15 acts as a valve seat for the plug 18. The apparatus 10 alsoincludes a pressure sensitive vent valve control means which includes anelastic diaphragm 20 stretched over a circular orifice 22 of the branch17, and a rigid wire rod 23 connecting the plug 18 to the centre of thediaphragm 20.

In this embodiment, the plug 18 is conical and the orifice 15 iscircular. In other embodiments (not shown), the plug and the orifice areother complimentary shapes.

The orifice 15 provides an outlet for the removal of gas upon patientexpiration. Gas removal is aided by the continuous flow of gaspressurised above atmospheric pressure flowing through the conduit 14and to atmosphere through the orifice 15.

As the air pressure in conduit 14 increases, corresponding increasesoccur in the air pressure adjacent diaphragm 20. These pressureincreases cause diaphragm 20 to bulge to the position represented byphantom line 26. The displacement of the centre of the diaphragm 20results in corresponding displacement in the plug 18, causing the plug18 to be drawn into the orifice 15 thereby restricting the flow of gasesthrough the vent orifice. In this way, the flow area of the vent isrestricted at higher delivery pressures thereby reducing flow of gasthrough the orifice 15 compared to a fully open orifice.

The apparatus can be calibrated by adjusting the length of the wire rod23 between the plug 18 and the diaphragm 20.

The vent valve apparatus 10 thereby maintains the airflow through thevent at, or at least near, the optimum safe minimum amount. This has theeffect of reducing the noise produced at higher CPAP pressures, comparedto the noise emitted by a similar orifice without the vent valve. Aquieter vent improves patient and bed-partner comfort. An additionalbenefit provided by the invention is the reduction in the amount ofwasted gas forced through the vent unnecessarily at higher CPAPtreatment pressures.

A prototype of the first embodiment of the invention shown in FIG. 1 hasbeen tested over a range of CPAP treatment pressures utilising thepresent Applicant's Sullivan™ V flow generator made by ResMed Limitedand Sullivan™ mask frame (fitted with Series 3 Sullivan™ BubbleCushion™) modified in accordance with the teaching of this invention.This prototype was also tested without the conical plug 18. The resultsof the tests are summarised in the table below: TABLE 1 PerformanceComparison for Prototype Vent Valve Apparatus With and Without theConical Plug With Without CPAP Pressure Air Flow Sound Pressure Air FlowSound Pressure cmH20 l/m Level dB (A) l/m Level dB (A) 4 11.2 34.1 11.936.1 10 14.4 46.8 19.5 48.4 18.5 9.0 52.7 26.7 55.7

As the results show, the prototype vent valve according to the firstembodiment of the invention maintained a substantially constant air flowthrough the vent over a wide range of CPAP treatment pressures comparedto the large variation exhibited by a similar mask without the conicalplug. Further, at all pressures, the noise produced by the mask usingthe vent valve apparatus according to the first embodiment of theinvention was less than the same mask without the conical plug.

Referring now to FIG. 2, there is shown a vent valve apparatus accordingto a second embodiment of the invention. Like reference numerals tothose used in FIG. 1 will be used to indicate like features in FIG. 2.This second embodiment functions in the same way as the first embodimentin that an increase in pressure in the conduit 14 causes the diaphragm20 to bulge and draw the plug 18 into the washout valve orifice 15,thereby restricting the flow of gas through thAT orifice.

A third embodiment of the present invention is shown in FIG. 3. Onceagain, like reference numerals are used to indicate like features. Thisthird embodiment includes an aerodynamic member, in the form of wing 30,which is disposed in conduit branch 17 and adapted to pivot about anaxis transverse to the direction of the gas flow along the conduitbranch 17. The wing 30 is connected to a pivot mechanism, indicatedgenerally at 31, which includes a connecting rod 33 and pivot joint 34.The connecting rod 33 and pivot joint 34 operatively corrects the plug18 to the wing 30. A spring 36 is used to bias the wing 30 and plug 18to a position where the flow area of orifice 15 is maximized. As gassupply 13 is forced through the conduit 14, branch 17 and over the wing30, the wing generates lift which opposes the spring and causesdisplacement of the wing to the position shown by phantom line 37,thereby drawing plug 18 into orifice 15 as shown by phantom line 32 and,thereby reducing the flow area of the gas washout orifice 15.Accordingly, the higher the pressure and flow rate of air passingthrough the branch 17 of the conduit 14, the more lift is produced bythe wing and the more the flow area of the washout vent orifice 15 isrestricted.

As with the earlier embodiments described above, this maintains asubstantially constant air flow through the washout vent orifice.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms.

1-25. (canceled)
 26. A vent assembly for use with a system forsupplying, from a gas supply, breathable gas pressurized aboveatmospheric pressure to a human or an animal, the assembly including: agas washout vent defining a flow area; a pressure sensitive controladapted to progressively restrict the flow area of the washout vent inresponse to increases in the pressure of the gas supply, therebysubstantially regulating the flow of gas through the washout vent over arange of gas supply pressures.
 27. An assembly as claimed in claim 26,further comprising a conduit in communication with the gas washout ventto provide a supply of pressurized gas.
 28. An assembly as claimed inclaim 27, wherein the gas washout vent is fixed with respect to theconduit.
 29. An assembly as claimed in claim 27, wherein the gas washoutvent is an orifice in the conduit.
 30. An assembly as claimed in claim27, further comprising a branch extending from the conduit, and whereinthe gas washout vent is an orifice in the branch.
 31. An assembly asclaimed in claim 27, further comprising a vent valve defining a plugmovable with respect to the conduit.
 32. An assembly as claimed in claim26, further comprising a vent valve including a plug connected to thepressure sensitive control such that movement of the pressure sensitivecontrol causes a responsive movement of the plug.
 33. A CPAP apparatusincluding a gas delivery system, a patient interface, and a ventassembly as claimed in claim
 26. 34. A vent assembly for use with asystem for supplying breathable gas pressurized above atmosphericpressure to a human or animal, the apparatus includes a gas washout ventdefined by an orifice, a vent valve having a shape complementary to theshape of the washout vent, the vent valve adapted to progressivelyrestrict the flow area of the washout vent, and a pressure sensitivevent valve control adapted to progressively cause said vent valve torestrict the flow area of the gas washout vent in response to increasesin the pressure of the gas supply, thereby substantially regulating thevolumetric flow of gas and or CO₂ through the washout vent over a rangeof gas supply pressures.
 35. An assembly as claimed in claim 34, whereina rim of the orifice acts as a valve seat for a cone shaped plug.
 36. Anassembly as claimed in claim 34, wherein the vent valve apparatus isprovided in a branch connection from a mask.
 37. An assembly as claimedin claim 34, wherein the vent valve apparatus is provided in an airsupply conduit substantially adjacent the mask.
 38. A vent assembly foruse with a system for supplying breathable gas pressurized aboveatmospheric pressure to a human or animal, the apparatus comprising: agas washout vent defining a flow area; a pressure sensitive vent controlincluding an elastic diaphragm stretched over a circular orifice,adapted to progressively restrict the flow area of the gas washout ventin response to increases in the pressure of the gas supply, therebysubstantially regulating the volumetric flow of gas and or CO₂ throughthe washout vent over a range of gas supply pressures.
 39. An assemblyas claimed in claim 38, further comprising a vent valve attached to thecenter of the diaphragm and a rod operatively connected to thediaphragm.
 40. An assembly as claimed in claim 39, wherein the rod isrigid, such that movement of the diaphragm is directly proportional tothe movement of the rod.
 41. An assembly as claimed in claim 38, furthercomprising a lever assembly connected to the diaphragm.
 42. An assemblyas claimed in claim 41, wherein the lever assembly includes a tensionerthat opposes the movement of the diaphragm caused by increasing gassupply pressure.
 43. An assembly as claimed in claim 42, wherein thetensioner comprises a spring.